Diagnostic Questionnaire

Accurate disease diagnosis can be difficult because the symptoms caused by Phytophthora ramorum are very similar to those caused by other fungi, insects, or adverse environmental conditions. The only way to confirm a P. ramorum or Sudden Oak Death infection is to take a sample and analyze the affected plant tissue in a laboratory.

There are two published diagnostic guides (Wildland Diagnostic Guide and Nursery Diagnostic Guide) to help you in assessing the likelihood of a P. ramorum infection on a plant and whether to send a sample to the laboratory for a confirmed diagnosis. The following question key can also be used to assist you, as well as the Misdiagnosis page.

Step One: Where Do You Live?

Is the tree in a county affected by P. ramorum ?

Infested Counties in California

Alameda

Mendocino

Santa Clara

Contra Costa

Monterey

Santa Cruz

Humboldt

Napa

Solano

Lake

San Francisco

Sonoma

Marin

San Mateo

Trinity

Counties not known to be currently infested, but are of concern include: Del Norte, San Luis Obispo and San Benito.

Step Two: Identify Type of Plant Affected

For help identifying oaks, visit the website of Steven Swain (UC Cooperative Extension, Marin County) on Oak Diagnosis, and the UC Davis Oak Woodland Management website. Also see the Host Plant List to see other types of plants that can be affected by P. ramorum.